The mouse ear swelling test is a well-accepted method for quantitating the inflammatory response to contact irritants and sensitizing agents. However, this assay measures edema rather than the cellular component of skin inflammation.
To develop a quantitative and noninvasive assay of inflammatory cell infiltration in contact dermatitis.
We bred a transgenic bioluminescent mouse that emits light proportional to cutaneous infiltration of inflammatory cells. We characterized this model by correlating luminescence with edema and histologic analysis of affected skin. A mouse strain expressing cyclization recombinase enzyme (cre) recombinase exclusively in myeloid cells was crossed with a reporter strain containing an inactivated form of the luciferase gene. In progeny mice, cre-mediated recombination repaired the luciferase gene, causing light emission from myeloid cells. Light emission and swelling from the inflamed ear was quantitated and compared to the contralateral ear.
Light intensity correlated with the inflammatory cell infiltration in the dermis. In sensitized mice challenged with squaric acid, luminescence increased about 2.2-fold while swelling increased about 1.5-fold.
Our model may serve as a useful screening assay for topical antiinflammatory molecules. Moreover, this approach allows real-time imaging of skin infiltration by specific inflammatory cell lineages in living animals.